This invention relates to archery bows and, in particular, to a bow handle made from a strip of extruded metal wherein the length of said handle is perpendicular to the direction of extrusion.
An archery bow is basically a two armed spring having a grip at the middle and held in a flexed or bent position by a string connected to each end of the spring. Energy stored in the bow as it is drawn is transferred to the arrow when the bow is fired. Despite the conceptual simplicity of a bow, actually making a durable, consistent bow has been the work of skilled craftsmen for millennia and continues today. The simplest bow is made from a single material, typically yew. Even this bow required careful tapering of the yew shaft to control curvature and draw force. Early composite or laminated bows of wood, horn, and sinew provided greater power and durability and permitted the maker to "recurve" the limbs, i.e. to curve the ends of the limbs away from the archer. A recurve bow can be made relatively short from end to end, yet have a long draw, that is, a large distance from the grip on the handle to the hock of the arrow at full draw.
Although laminated wooden bows are still made today by a few dedicated craftsmen, the modern bow is typically made in three sections: a central handle or riser and two separate limbs. The handle is typically made from cast aluminum or magnesium. In the last couple of years, handles have also been made by milling a rectangular aluminum block or billet in a computer controlled milling machine. As understood by those skilled in the art, references to elemental metals does not imply any degree of purity; all bows are made from commercially available alloys of the named metal.
Whether a bow be prehistoric or modern, the central problem is to make the bow sturdy enough to withstand the large forces resulting from repeatedly drawing and firing the bow. The problem is more acute in the modern "compound" bow in which pulleys are attached to the free ends of the limbs and laced with cable to give the archer a mechanical advantage in drawing the bow. When the pulleys are mounted eccentrically, rotation of the pulleys increases the effective length of the limbs at full draw, reducing the required draw force (known as draw weight or simply weight). A reduced weight at full draw permits the peak weight of the bow to be increased even more.
Because of the mechanical advantage resulting from the use of pulleys in a compound bow, limbs are much stiffer, thereby increasing the forces on the handle. Cast metal handles tend to have a more porous structure than handles machined from a billet, requiring that the casting be somewhat thicker than theoretically necessary.
For the modern commercial bowmaker, another problem is the cost of making the handles. Cast and machined metal handles are expensive to manufacture. Mold sets for casting a handle can cost many tens of thousands of dollars and wear out. Re-conditioning the molds is almost as expensive as making new ones. In addition, a different set of molds is required for each shape of handle. Some savings can be achieved in using split molds to make left and right hand versions of a handle, but the cost is still great.
Machining a billet obviates the need for molds but requires a large investment in equipment. In addition, machining a handle from a billet takes a long time because a large volume of material must be removed to produce the complex shape of a handle. A handle may have a nominal thickness of three-quarters of an inch but, because of the bends in the handle, the billet must have a thickness of more than two inches. Removing the excess material generates a large amount of scrap which must be collected, stored, and recycled. In addition, tool bits become worn and must be replaced. Time and material costs are high because the handle uses less than fifty percent of the billet.
Despite these disadvantages, machining a billet is being increasingly used among manufacturers because one can produce virtually any shape handle from a billet. In addition, features, such as pockets for an arrow rest and a sight, can be machined into a handle more accurately than they can be cast.
In general, it is desired to combine the materials savings of casting with the accuracy and flexibility of machining a billet.
It is therefore an object of the invention to more efficiently produce metal handles for archery bows.
A further object of the invention is to be able to produce many shapes of bow handles from extruded blanks having the same shape.
Another object of the invention is to be able to produce left and right hand versions of a bow handle from the same shape blanks.
A further object of the invention is to reduce the time required to produce a machined handle for an archery bow.
Another object of the invention is to reduce the amount of excess material which must be removed to produce a machined handle for an archery bow.